Current storage arrays (or controllers) make limited use of a controller cache. In a write through cache policy mode an input/output (IO) write request has to depend on the response time of the particular hard disk drive (HDD). In a heavy IO request storage array network (SAN) environment, the HDD response time is even further delayed. In an IO read-ahead cache policy, unwanted data is fetched which results in a direct read-to-HDD, with a delay corresponding to the HDD response time. The time consumed in the unwanted data fetch is wasted.
Write caches and read caches stored on DRAMs depend on writing to the HDD for the write through cache policy when there is no back-up battery for the caches. Writing to the HDD for the write through cache policy adds to the latency of the HDD. The read-ahead cache policy does not help reduce the latency of the HDD since the pre-fetch results of unwanted data adds to the time delay in getting the write data.
It would be desirable to implement a method and/or apparatus for reducing drive overhead using a mirrored cache volume in a storage array.